This invention relates to heat exchangers, and more particularly relates to the design of and methods of forming heat exchange elements which may be usable for a variety of purposes in the construction of heat exchange units such as, for example but not confined to, water radiators and oil coolers for internal combustion engines (e.g. in vehicles), solar heat collectors,milk coolers and the like.
One object of the present invention is to provide an element for use in heat exchanger constructions and applications, capable of being manufactured simply and at relatively low cost.
According to one aspect of this invention therefor, there is provided an element for use in a heat exchange system comprising a cylindrical tube member formed by a moulding or extrusion process from a heat resistant substantially rigid setting plastics material, said member having a smooth bore and an integrally formed helical external fin extending along at least a major part of its length.
Another object of the invention is to provide a heat exchange unit which is effective in operation and capable of being manufactured relatively simply and economically. Accordingly, in a second aspect there is provided a heat exchange unit comprising a pair of elongate manifold members of a heat resistant and substantially rigid plastics material,conjoined by a plurality of duct members formed by a moulding or extrusion process from a heat resistant and substantially rigid setting plastics material and each being of cylindrical tube form with a smooth bore and with an integral helical external fin extending along at least a major part of its length, the ends of said duct members opening into the manifold members for communication therebetween.
The invention further provides the methods and means of forming the elements and complete heat exchange units, and other and more particular objects and advantages of the invention will become apparent from the ensuing description.
It is well known to provide tubular fluid ducts with helically formed fins thereon for use in heat exchange units, but conventionally the two usually adopted known methods of forming such heat exchange elements or duct members involve in one case the provision of a separate pre-formed cylindrical tube element and the subsequent fitment on such element of a separately formed helical fin member, with the fin member being maintained in place by friction; or in the second method a pre-formed and set tubular element is provided and a helix is formed on the outer surface thereon by such as the application of special rollers to the outside of the tube to deform the metal or other material, under pressure applied by the rollers. Both methods of constructing known helically finned tubing elements can be relatively expensive and slow, and involve the employment of pre-formed lengths of tubing,whereas the present invention provides that a tubular heat exchange element or duct member incorporating an integral helically formed cooling or heat exchange fin is simply and economically provided by direct extrusion or moulding of a suitable plastics material that will be substantially rigid once set and can be manufactured in a continuous or any prescribed length and for subsequent severing in required short lengths.
The previously referred to method of forming helical fins utilizing externally applied rollers under pressure can lead to uneven or occasionally broken fin formations, or fin formations of a fragile nature and/or a weakening of the tube as a whole (sometimes necessitating the provision of an inner strengthening tube) due to the deforming of the material, and in some cases resultant work hardening of the material, whereas the formation of the plastics elements or duct members of this invention by an extrusion or moulding process provides an integrally formed fin which is easily formed to any desired thickness or cross-section whilst maintaining its desired strength and without any stress being placed on, or weakening of, the main cylindrical tube part of the element or duct member.
The term "heat resistant plastics" as used herein means a plastics material such as a thermo plastic polymer material, that once set and hardened is capable of withstanding relatively high temperatures without the plastics material breaking down or deforming. One preferred application of the present invention is in the formation of water cooling radiators for internal combustion engines e.g. in motor vehicles, and the plastics material utilized must therefore be able to withstand the anticipated maximum heat variations, as well as pressure variations to which a normal internal combustion engine radiator is subjected; and some examples of suitable or possibly suitable plastics materials having the required heat resistance, workability and strength characteristics include those manufactured and sold under the registered Trade Marks ARNITE, UDEL, VITREX and ULTEM.